W32.Weird

SUMMARY

This virus infects files in the Windows and WindowsSystem folders.

Protection

• Virus Definitions (LiveUpdate™ Weekly) July 6, 1999
• Virus Definitions (Intelligent Updater) July 6, 1999

Threat Assessment

Wild

• Wild Level: Medium
• Number of Infections: 50 - 999
• Number of Sites: More than 10
• Geographical Distribution: High
• Threat Containment: Moderate
• Removal: Easy

Damage

• Damage Level: Low
• Modifies Files: Windows .EXE files, Wininit.ini
• Compromises Security Settings: May allow unauthorized access to your computer

Distribution

• Distribution Level: Low
• Target of Infection: Windows .EXE files

TECHNICAL DETAILS

W32.Weird creates a hidden process that opens an IP port and listens for commands. This hidden process is similar to other client/server Trojan horses such as NetBus, Backdoor, and BackOrifice. Upon execution of an infected file, W32.Weird creates a file with 10 KB of viral code in the Windows folder. The name of this file is based on the computer name of the infected system. This 10-KB file contains the server application.

NOTE: This virus will locate Windows even if it is installed to a location other that Windows. If that is the case in your situation, make the appropriate substitution when reviewing the information in this document.

The virus then creates a copy of Explorer.exe in the in the Windows folder. The new file has the same file name, different one-character extension, for example, Explorer.3. This new file is infected.

Next, W32.Weird creates a Wininit.ini file that contains a command to rename the infected version of Explorer to Explorer.exe. When Windows is restarted, the infected version of Explorer is executed.

Windows 2000
Additional information for users of Windows 2000 only:
The virus does not appear to properly infect Windows 2000 systems. When executed on such a system, it does not create the 10 KB viral file in the Winnt folder, but it does create the viral copy of Explorer.exe in the Windows folder. It also creates the Wininit.ini file which is supposed to rename Explorer.exe when Windows is restarted. However, when the system actually restarts, the file does not get renamed as intended, and the Wininit.ini file is still present.

Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

• Turn off and remove unneeded services. By default, many operating systems install auxiliary services that are not critical, such as an FTP server, telnet, and a Web server. These services are avenues of attack. If they are removed, blended threats have less avenues of attack and you have fewer services to maintain through patch updates.
• If a blended threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
• Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services (for example, all Windows-based computers should have the current Service Pack installed.). Additionally, please apply any security updates that are mentioned in this writeup, in trusted Security Bulletins, or on vendor Web sites.
• Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread viruses, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate infected computers quickly to prevent further compromising your organization. Perform a forensic analysis and restore the computers using trusted media.
• Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.

REMOVAL

To remove this virus:

NOTE: Removal of this virus requires that you have a DOS boot disk or Windows Startup disk, and assumes that you be familiar with using basic DOS commands at the command prompt.

1. Insert a clean DOS floppy disk or Windows Startup disk into the floppy disk drive, and restart the computer.
2. At the prompt type the following two commands, pressing Enter after each one:
   
   c:
   cd windows
   dir *.exe /a:h
   
   All .exe files in the Windows folder that have the hidden attribute are displayed.
   
   NOTE: If Windows is installed in a different location, make the appropriate substitution when typing the first command.
   
3. Look for a file with a size of 10,240 bytes. The name of the file is generated by taking the computer name on the infected system and changing some of the characters. Write down the name of this file.
4. Type the following, and then press Enter after each one:
   
   attrib <file name from step 3> -h
   del <file name from step 3>
   
5. Type the following two commands, pressing Enter after each one:
   
   del wininit.ini
   del wininit.bak
   
6. Restart the computer.
7. Start Norton AntiVirus, and run LiveUpdate.
8. Run a full system scan. Attempt to repair any files that are infected with W32.Weird. If they cannot be repaired, you must delete them and restore them from a clean backup copy, or reinstall the deleted file.
   
   NOTE: If NAV reports that it cannot delete an infected file, you must shut down the computer, turn off the power, and wait 30 seconds. Then restart the computer in Safe mode and run the scan again. All Windows 32-bit operating systems except Windows NT can be restarted in Safe mode. For instructions on how to do this, read the document How to start the computer in Safe Mode.